Historically, processing pliant materials such as rubber compounds and elastomers has presented serious difficulties. This has been especially true when the processing resembled grinding to shape or finish a part as practiced on hard materials such as metals, thermosetting resins and the like. The resilience of the workpiece has produced a variable and unpredictable interface between workpiece and tool and consequent unpredictable dimensions and surface finish of the workpiece. Furthermore, the nature of the debris from the workpiece produced by a grinding operation on pliant materials presented other serious problems in productivity and product quality. Specifically, using a grinding wheel or similar grinding tool incorporating relatively large abrasive particles on the grinding surface results in excessive forces on the workpiece and consequent distortion of the product during processing, low quality and difficult quality control. On the other hand, smaller abrasive particles that do not abuse the workpiece to the same extent tend to clog the grinding surface which quickly becomes non-functional because of the debris retained on the wheel.
For many grinding applications involving pliant workpieces, a grinding tool made in accordance with Neff U.S. Pat. No. 5,181,939 optimized both the speed with which a workpiece can be finished as well as the quality of the finished product. In accordance with the teaching of the '939 patent, elements of a generally conic configuration made up of many small abrasive particles are held together on a flexible matrix, transferred to a tool blank and brazed in place to form a finished tool. The tool may be in the nature of a hand file, a rotary grinding wheel or other appropriate configurations. The conic elements can be dressed to provide a precision grinding surface and the interstices between the apices of the elements provide the capability of receiving grinding debris and discharging that grinding debris from the working face.
While grinding tools for many applications have been very successful utilizing the teachings of the '939 patent, certain workpieces requiring a relatively high degree of precision and high production rates were not readily produced even with the advantageous processes and products provided by the '939 teaching. However, the teaching of the '939 patent is utilized in the preferred embodiments of the invention described hereinafter and the entire specification and drawings thereof are incorporated herein by reference.
One product that has heretofore escaped the full benefits of the abrasive element and tool construction of the '939 patent are automotive accessory belts and similar pliable products having one or more grooves to receive corresponding ribs in pulleys and the like. Automotive accessory belts have multiple grooves formed in the cross section to receive the ribs on the circumference of multi-rib pulleys that either drive the belt or are driven by the belt to power air conditioning systems, power steering systems and the like. The multiple grooves in automotive accessory belts have been molded, or alternatively, they have been formed in flat belts using grinding or flycutting techniques. Grinding has been achieved using wheels surfaced with small diamond particles and having the profile for the multiple lands and grooves of workpieces formed therein. In flycutting, a term adopted from the metal working industry, tungsten carbide knives are held in a rotating fixture. The knives are ground to produce the desired belt profile.
Both the grinding and flycutting techniques present problems, produce imprecise results and involve short tool life and high cost. In diamond grinding wheels, very fine diamonds must be used to achieve the intricate profile in the belt. Consequently, the material removal rate is limited as are the speeds and feeds. Surface speeds with conventional belts have normally been limited to less than 6,000 feet per minute and the rate at which the belt can be fed is limited to about 90 feet per minute. Flycutting with tungsten carbide knives offers great advantages in productivity. Speeds in the order of 10,000 feet per minute are possible and a feed rate in the order of 5 inches per second has been reported. However, the flycutting tools have very short useful life and frequent resharpening is required. This necessitates constant process monitoring and downtime for removing and replacing tooling. Consequently, tooling costs for both diamond grinding and flywheel cutting have been high.